Currently there exist no bicycle accessory that can measure the cyclist power output without requiring bike disassembly and significant modification to the existing components on the bike. This generally requires a bike mechanic to make this change and can be costly. Also this generally requires, some custom version of a large mechanical and expensive part of the bike, such as the pedal crankshaft or rear wheel hub. Other products include chain tensioners in their design—again expensive, unreliable and intrusive. The device described in this document does not have these drawbacks. I arrived on the idea of this device invention while pondering what I might show at an upcoming “Maker Faire” in San Mateo Calif. in May 2012. It is a result of an interest in bicycling, mobile technology and having a friend, with whom I was co-sponsoring a “Meetup” and spent time with discussing automobile gas mileage measurement though the automobile CAN bus. This invention is a result of a convergence of those ideas and activities.